The present invention concerns spinal instrumentation systems, such as for use with the cervical vertebrae. More particularly, the invention pertains to a plating system for use in treatment of the cervical spine.
Within the last decade, the use of fixation plates for treatment of spinal disorders or for fusion of vertebrae has grown considerably. While early procedures using fixation plates were at the lower lumbar levels, spinal fixation plates have recently found applications in the instrumentation of the cervical sphine. Successful spinal instrumentation in this region is particularly difficult given the problems of safely accessing the instrumentation site.
The upper cervical spine can be approached either anteriorly or posteriorly, depending upon the spinal disorder to be treated. Many of the well known surgical exposure and fusion techniques of the cervical spine are described in the publication entitled Spinal Instrumentation, edited by Dr. Howard An Dr. Jerome Cotler, particularly at pages 1-11. Of particular relevance to the present application are the exposure techniques and procedures for the anterior approach described at pages 1-5 of this publication, which disclosure is incorporated herein by reference. In this text, as well as in other documentation describing cervical spine surgical techniques, it is stressed that complications associated with the procedure can be devastating, such as injury to the brain stem, spinal cord or vertebral arteries. In addition, a lengthy procedure can lead to typical surgical complications.
On top of the normal complications associated with exposure and fusion of the cervical spine, implantation of a spinal fixation plate adds to the degree of risk and complication. In one cervical plating system of Synthes, Inc., the steps of a known fusion and instrumentation procedure are described. In this procedure, it is necessary to locate the fixation plate over the vertebral levels to be instrumented and use this plate as a drill guide for drilling and tapping the bone in preparation for receiving a fixation screw. The Synthes system and procedure provides for a soft tissue protector in the manner of an elongated sleeve which is intended to minimize damage to the surrounding muscle and other tissues.
There is a need for a cervical plating system which minimizes the intrusion into the patient and reduces trauma to the surrounding soft tissue. Moreover, a system is required that allows for easy access to drill and tap the cervical vertebral with little room for error in positioning the fixation screw.
Even as the cervical spine instrumentation techniques can be improved, so can the manner of fixation of the plate to the affected vertebral levels. For example, the Synthes locking plate accepts spinal screws at several locations at the ends and in the middle of the plate. In each case, the screws are not capable of varying degrees of fixation between the vertebra and the plate. In addition, the Synthes device utilizes a locking screw which is threaded into the expansion head of the vertebral fixation screw to lock the screw into the plate. This procedure requires a locking screw for every fixation screw, thereby lengthening and complicating the procedure.
There therefore remains a need for a cervical plating system which provides for a wider range of fixations at the different vertebral levels. The need also extends to a plating system which minimizes the steps required to provide firm fixation of the spinal screws to the plate. Other requirements for an optimum cervical fixation system addressed by the present invention are disclosed herein as the components of the system are described.